The invention relates to a workpiece holding means for machine tools and more particularly for milling and/or drilling machines, comprising a pivoting bridge more particularly possessing two bearing pins for the pivotal support between two bearing walls respectively laterally delimiting a working area, and furthermore at least one drive motor for pivoting the pivoting bridge, such motor being arranged outside the said working area on at least one outer side of the bearing walls.
The use of such pivoting bridges as workpiece holding means for machine tools is for example disclosed in the European patent publication 0712682 or in the German patent publication 3,624,284 C2. The drive motor is in each case arranged externally on one of the two bearing walls, i.e. clear of the working area in order to protect same from shavings produced in the course of machining and from lubricating substances and coolants. This externally mounted drive motor drive drives, at this position, one of the bearing pins so that same must transmit the entire driving torque from the bearing pin to the pivoting bridge. More particularly in the case of high precision machining the torque on the bearing pin has turned out to be disadvantageous, since effects are produced on the accuracy of positioning and the running behavior.
One object of the invention is to so improve a workpiece holding means of the type initially mentioned that if the drive motor is externally mounted torque forces on the bearing pins may be prevented.
In order to achieve these and/or other objects appearing from the present specification, claims and drawings, in the present invention the pivoting bridge is provided with a gear ring at one or both of the two inner sides of the bearing walls, such gear ring being drivingly connected with a drive gear wheel itself driven by the at least one drive motor.
There is the advantage that not only a bearing pin but also the pivoting bridge is driven directly by way of its gear ring so that there is a short power transmission path and no torque load on the bearing pins. This leads to improved running properties and to a greater accuracy of positioning. As regards precise bearing means the bearing pins may be optimized without paying heed to the drive means.
The measures recited in the claims represent advantageous further developments and improvements of the invention.
The drive motor and/or a drive shaft driven by it and provided with a drive gear wheel extend at least partially from the outside through the bearing wall. This means that simple dismounting of the drive for the pivoting bridge is possible, for example by detaching the drive motor from the bearing wall and drawing it outward together with the drive gear wheel.
The gear ring and the drive gear wheel are preferably in mesh with each other or connected together by way of a drive train such as a sprocket chain or a toothed belt.
In an advantageous form of the invention the drive gear ring extends into an annular or disk-like recess in the inner side of the bearing wall at least partially so that it is substantially protected against matter produced in the course of machining such as shavings or the like.
In accordance with an advantageous design of the invention the drive gear ring is attached to of formed on a disk-like area of the pivoting bridge and more particularly on a flat side thereof facing the bearing wall. The disk-like area accordingly serves not only as a holding socket for the gear ring but also additionally for screening off from the working area, more especially in the case of an arrangement of the gear ring let into the bearing wall.
In order to achieve an even better sealing effect for the gear wheel drive to shut it off from the working area it is an advantage to arrange a seal ring for sealing the drive gear ring and/or the drive gear wheel between the disk-like area of the pivoting bridge and the inner side of the corresponding bearing wall, the face of engagement between the sealing ring and the disk-like area or the inner side of the bearing wall preferably being in the form of a plain bearing means and/or a labyrinth seal face. Accordingly it is possible for the gear ring or, respectively, the drive gear wheel to be reliably protected or sealed from liquids and lubricants required for machining.
In accordance with an advantageous development of the invention at least one of the bearing pins, which are more especially supported in bearing sleeves, contains a concentric, motor-driven drive shaft, which drives, by way of an power transmission train, running in or on the pivoting bridge, at least one workpiece table supported in a rotatable manner on the pivoting bridge. Such a drive, which in principle is disclosed in the initially mentioned prior art, for a workpiece table through the bearing pin can be designed for substantially more simply, if in accordance with the invention the bearing pin is not required from the pivotal drive of the pivoting bridge.
The drive motor for the drive shaft in the bearing pin is secured to the latter in a manner preventing relative rotation so that the pivotal motion of the pivoting bridge is decoupled for the rotary movement of the workpiece table.
The torsion force acting on the pivoting bridge may be further reduced if the pivoting bridge has two gear rings at the inner sides of the two bearing walls and if two drive motors are provided for a synchronous drive of such two gear rings.
The diameter of the gear ring is preferably substantially larger than the diameter of the drive gear wheel, something which contributes to increasing precision of positioning of the pivoting bridge. Furthermore, for the drive motor a transmission with an extremely low step-down transmission ratio may be selected, or it is even possible to completely do without such a step-down transmission.
Further advantageous developments and convenient forms of the invention will be understood from the following detailed descriptive disclosure of one embodiment thereof in conjunction with the accompanying drawings.